Today's forests reserves include, in a number of areas, small diameter trees previously considered uneconomic for use in producing lumber. By small diameter is meant trees ranging from about 2 inches to about 8 inches in diameter. Also pieces of lumber have normally been produced from logs 16 feet in length. On small trees, however, it is not normally possible to get a 16 foot length suitable for conversion to lumber and thus it becomes necessary to produce pieces of lumber from logs of shorter length.
There is thus a need for equipment to be able to produce pieces of lumber from logs of relatively short length and also from logs that are relatively small in diameter. To be competitive it is also necessary to produce pieces of lumber from such logs in an economic manner and also produce quality chips.
It is known to produce chips when reducing a log from a squared piece of timber and by way of example reference may be had to U.S. Pat. No. 3,780,778 issued Dec. 25, 1973 to F. Chapman. This patent discloses a sawing and chipping machine.
In reducing a log to pieces of lumber it is well known to propel a log endwise through different pieces of machinery that perform different functions on the log as it is propelled. U.S. Pat. No. 5,143,127 issued Sep. 1, 1992 to K. Rautio discloses apparatus to propel and guide a log endwise along a predetermined path between a pair of spaced apart oppositely disposed chipper heads to produce chips and a pair of opposite parallel flat faces. Downstream from the chipper heads are circular saws with chipper edgers that produce pieces of lumber. Downstream from the saws are vertically disposed divider units that are aligned with the saw blades. In this apparatus the log is supported from below by a fixed in position slide rail and the cant chipper heads provide only two flat faces with such faces being in parallel vertical planes.
Squaring a log using a first pair of chipper heads and a second pair of chipper heads downstream from the first pair is known as for example from the teachings of Canadian patent issued Mar. 3, 1987 to K. Rautio. This patent also discloses sawing the squared timber into pieces of lumber by saws mounted on a frame that is pivotally supported the purpose of which is curve sawing.
Canadian patent 1,131,551 issued Sep. 14, 1983 to K. Rautio discloses first and second pairs of cutter heads and log propelling means mounted on a common frame for producing a squared timber piece from a log. The patentee mentions that circular saw blades may be provided for cutting the squared timber piece into "one or several parts".
There is no mention or suggestion in the foregoing prior art of squaring the log to a first selected dimension and rabbetting the corners to maximize the lumber obtained from a given tree size or given range of tree sizes.
Canter chippers are known and by way of example reference may be had to PCT/SE92/00063 published Aug. 20, 1992 under international publication number WO92/13685. Disclosed in this PCT application is a chipper head in the form of a truncated cone with replaceable cutters mounted thereon.